Process of producing diazotype paper



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No Drawing. Filed Aug. 8, 1958, Ser. No. 753,802 8 Claims. (Cl. 117-34) This invention relates to a process of producing diazotype paper having a reduced tendency to curl, improved development characteristics, increased density, as well as other desirable qualities such as better feel, rattle and bulkiness.

As is well known, diazotype materials having a paper base coated on one side with a light-sensitive diazotype composition have a tendency to curl after being wetted as after development. To counteract this tendency to curl, it has already been proposed to coat the back side of the paper with various water-soluble resins, natural gums or inorganic salts. Wetting the back of the paper with water alone has also been proposed for this purpose. The particular type of paper used as the base also has an effect upon development. Thus, it was found that better development is obtained when the base is made of paper which is highly calendered to have a very smooth surface and highly compacted so as to have a very low gas permeability. It was found, however, that paper which has been highly calendered has a greater tendency to curl than does paper which is not so highly calendered.

It is, accordingly, an object of this invention to provide a process for producing a diazotype paper having a greatly reduced tendency to curl, greatly improved de velopment characteristics and greater density.

It is a further object of this invention to provide a process for producing a diazotype paper having greatly improved development characteristics and density by coating the back and front sides of the paper in a particular sequence of steps.

Other objects and advantages of this invention will become apparent to those skilled in the art from the detailed description given below.

We have found that if a highly calendered paper having a low gas permeability or porosity, as, for example, a paper having a porosity of 100 on the TAPPI scale, is first coated with a water-soluble, film-forming material on the back side thereof, dried and thereafter coated on the front side thereof with a light-sensitive composition containing a light-sensitive diazo compound, greatly improved development characteristics, image density, r-attle, feel and bulkiness are imparted to the paper. Porosity on the TAPPI scale is defined as the number of seconds required to force a given volume of air through a given volume of paper under certain specified conditions. (TAPPI MethodT-460m46.) This order of steps is critical since if this order is not followed, the improved results stated above are not obtained.

We have tried first coating the front side ofthe paper with the light-sensitive diazo composition, drying and thereafter coating the back thereof with a water-soluble, film-forming material. The development characteristics, image density, etc. of the thus coated paper were found, in fact, to be inferior to a diazotype paper having no coating on the back thereof.

We have also tried coating the front side of the paper with the diazotype composition and immediately thereafter, and before drying, coating the back of the paper with the water-soluble, film-forming material. The results upon development were as unsatisfactory as those ted States Patent G Patented July 25, 1961 obtained by the process described in the preceding paragraph.

Another method tried by us was to first coat the back of the paper with a solution of the water-soluble, filmforming material and immediately thereafter, and before drying, coat the front side with a diazotype composition. The results upon development were also unsatisfactory.

The exact reason for the beneficial results obtained by our process is not known. Our theory is that whenever the diazo-type composition is placed on the paper when the latter is wet or the paper is wetted after the diazoe type composition is placed thereon and before exposure, the diazotype composition diffuses into the body of the sheet which results in impaired development, lowered density and a flat, washed-out looking print. We do'not intend to be bound by this theory, however. Whatever the reasons, the fact is that by following the steps of our novel process as outlined above, we obtained a new and unexpected improvement in the development characteristics, density, etc. of the diazotype paper.

We have also attempted to mix the water-soluble, filmforming material with the diazotype composition and then coat the mixture on the front of the paper. The results were unsatisfactory. The development characteristics and density were not as good as with a paper Where no film-forming material was used.

We also attempted to coat the front face of the paper with a coating of the water-soluble, film-forming material and overcoating the same with the light-sensitive diazotype composition. .The results were also unsatisfactory. It appears that the vapor barrier produced by the filmforming material should not be too close to the sensitized surface but rather that there be a more or less deep pocket which can act as a reservoir for the ammonia gas absorbed during development.

An example of our novel process is given below. It is to be understood, however, that this example is given by way of illustration and not by way of limitation.

Example A highly calendered sheet of paper having a very smooth' surface and a porosity reading of over (TAPPI) was coated on the back side with a. 5% water solution of gelatin and the paper dried. After drying, the front side (felt side) was coated with the following lightsensitive solution and dried:

Water to make 100.0 cc.

The thus coated paper was exposed, under an original, to actinic light and developed in the ammonia chamber of a white-print ammonia development machine in the usual manner. In addition to the expected improvement in the curl characteristics of the paper due to back coating with the gelatin, there was a remarkable and wholly unexpected improvement in the development characteristics of the paper and in the density of the image produced over the development characteristics and image density of uncoated paper. There was also a great improvement in the feel, rattle and bulkiness over that of uncoated paper.

Following the procedure outlined in the above example, we coated samples of high density paper with anaqueous solution of any one of the following filmforming materials: hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, carboxymcthyl hydroxyethyl cellulose and sodium cellulose sulfate instead of the gelatin as in the example. The results obtained by the use of any one of these materials were substantially the same as those obtained by the use of gelatin. We found that solutions having concentrations of l-5% of these film-forming materials give the best results.

It. is to be understood that in lieu of the 2,3-dihydroxynaphthalene-6-sulfonic acid coupler of the example, other couplers may be used such as 2-amino-8-naphthol-3,6- disulfonic acid, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,7-amino-naphthol-2-hydroxy-8-biguanide, resorcinol, phloroglucinol, m-hydroxyphenyl-urea, aceto acetanilide, 7-hydroXy-1,Z-naphthimidazole and the like.

Furthermore, instead of the particular diazo mentioned in the example, diazos may be employed which are derived from any of the usual p-aminophenylenediamines. Examples of such diazos are those from pamino-N- methylaniline, p-amino-N-dimethylaniline, p amino-N- ethylaniline, .p-amino-N-hydroxyethylaniline, p-amino-N- ethyl-N-hydroxyethylaniline, 4-amino-2-methoxy-1-cyclohexylaniline and the like.

Modifications may be resorted to within the scope of the appended claims.

We claim:

1. A process of producing a light-sensitive diazotype paper which comprises first coating one side of a highly calendered smooth surfaced paper having a porosity of about 100 on the TAPPI scale with an aqueous solution of a water-soluble, film-forming material, selected from the group consisting of gelatin, hydroxyethyl celluloSe, carboxymcthyl cellulose, methyl cellulose, carboxymethyl hydroxyethyl cellulose, polyvinyl alcohol and sodium cellulose sulfate, drying the paper and thereafter coating the other side of the dried paper with a solution of light-sensitive diazotype composition and drying.

2. A process as recited in claim 1 wherein the Watersoluble, film-forming material is gelatin.

3. A process as recited in claim 1 wherein the Watersoluble, film-forming material is hydroxyethyl cellulose.

4. A process as recited in claim 1 wherein the watersoluble, film-forming material is carboxymethyl cellulose.

5. A process as recited in claim 1 wherein the Watersoluble, film-forming material is methyl cellulose.

6. A process as recited in claim 1 wherein the watersoluble, film-forming material is carboxymethyl hydroxyethyl cellulose.

7. A process as recited in claim 1 wherein the watersoluble, fihn-forming material is polyvinyl alcohol.

8. A process as recited in claim 1 wherein the watersoluble, film-forming material is sodium cellulose sulfate.

References Cited in the file of this patent UNITED STATES PATENTS 1,641,401 Sulzer Sept. 6, 1927 2,008,984 Kenydon July 23, 1935 2,036,387 Babcock et al. Apr. 7, 1936 2,476,240 Famulener July 12, 1949 2,495,661 Scanlan Jan. 24, 1950 2,536,656 Petroske Jan. 2, 1951 2,646,366 Baxter July 21, 1953 2,778,735 Brinnick et a1. Jan. 22, 1957 2,805,159 Unkauf Sept. 3, 1957 

1. A PROCESS OF PRODUCING A LIGHT-SENSITIVE DIAZOTYPE PAPER WHICH COMPRISES FIRST COATING ONE SIDE OF A HIGHLY CALENDERED SMOOTH SURFACED PAPER HAVING A POROSITY TO ABOUT 100 ON THE TAPPI SCALE WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLE, FILM-FORMING MATERIAL, SELECTED FROM THE GROUP CONSISTING OF GELATIN, HYDROXYETHYL CELLULOSE, CARBOXYMETHYL CELLULOSE, METHYL CELLULOSE, CARBOXYMETHYL HYDROXYETHYL CELLULOSE, POLYVINYL ALCOHOL AND SODIUM CELLULOSE SULFATE, DRYING THE PAPER AND THEREAFTER COATING THE OTHER SIDE OF THE DRIED PAPER WITH A SOLUTION OF LIGHT-SENSITIVE DIAZOTYPE COMPOSITION AND DRYING. 